At present, in an era of communications by satellite, stations which can communicate with multiple satellites and multiple frequency bands per satellite simultaneously are increasing in number. These stations include, for example, Cable TV stations and other television stations. Because each of these stations may communicate with dozens of satellites simultaneously, it is very inconvenient to incorporate antennas which are only capable of communicating with a single satellite. Therefore, it is highly advantageous for these stations to incorporate antennas which are capable of receiving and/or sending signals to multiple satellites simultaneously.
The main antenna being used today and capable of communicating with a plurality of satellites simultaneously is an antenna called "Simulsat" for Simultaneous Multiple Satellite Antenna Terminal. Simulsat has an elongated reflector which is constructed with a circular cross-section in the horizontal plane and with a parabolic cross-section in the vertical plane (generally referred to as quasi-parabolic). The size of the reflector for a small Simulsat antenna is 16 feet by 28 feet and the entire structure weighs 2000 pounds. Because of the size, the reflector is constructed in sections, typically three, which must be assembled at the sight.
It will be understood, by those skilled in the art that the communications satellites used in these applications are synchronous orbit satellites positioned generally in the equatorial plane. Thus, antennas incorporating a plurality of feeds for receiving signals from a plurality of satellites, position the feeds in a line spaced from an antenna reflector. The antenna must then be positioned so that each feed receives signals from a different satellite. Because of the elongated construction and the size, at different positions on the Earth's surface the Simulsat antenna must be rolled farther from the horizontal to compensate for the curvature of the Earth. To accomplish this positioning of the antenna, the structure must be mounted higher and higher above the ground so that the corner is sufficiently far from the ground.
As will be understood by those skilled in the art, the enormous size and weight of the Simulsat antenna causes many problems in mounting and directing it correctly. Also, the initial cost of the antenna is high and the mounting problems add substantially to the cost. Up to 35 feeds can be employed with this antenna. However, the cost will be the same for smaller stations that only want 10 or 12 feeds as for large stations that want up to 35 fees. Further if a station wants 36 or 37 feeds it must add a complete new antenna with all of the costs and mounting problems involved.
A second, less popular antenna is called the Taurus Antenna. This antenna is extremely large, heavy, and expensive. Also, it is designed, like the Simulsat antennas, for receiving only C-band signals from satellites.
When the Simulsat and Taurus antennas were originally designed, most of the communication satellites transmitted only C-band frequencies, commonly 3.7 GHz to 4.2 GHz. Kuband, commonly 11.7 GHz to 12.2 GHz, was added later in the 1980's to meet the demand for more bandwidth. Most of the current synchronous orbit satellites transmit both C-band and Ku-band signals. Also, during the 1990's the Federal Communications Commission (FCC) decreased the satellite spacing from four and one half degrees to two degrees to meet the demand for more bandwidth. This actually made the multiple feed application on a parabolic dish more desirable since the placement of second and third feeds two degrees away from the boresight feed will perform with only insignificant degradation. It should be noted that, throughout this disclosure, a reference to antenna feed positions or locations two degrees (or two degrees off boresight), four degrees, six degrees, etc. is a reference to the spacing of the satellites from which the feeds are receiving signals. Thus, a first feed positioned at the boresight will receive signals from a first satellite and a second feed spaced "two degrees" from the first feed will receive signals from a second satellite spaced two degrees from the first satellite, etc.
To date, no single prior art satellite communications parabolic reflector antenna in the 12 to 16 foot range has been able to incorporate multiple antenna feeds positioned adjacent each other which can receive both C-band and Ku-band signals from three or more satellites spaced two degrees apart. Previously, as will be explained in more detail presently, some C-band feeds have been constructed which can be positioned two degrees apart. However, these antenna feeds receive C-band only and cannot be modified to simultaneously receive Ku-band signals. The Simulsat and Taurus antennas perform acceptably well at C-band, however, due to a circular curvature or cross-section, rather than parabolic, in the horizontal plane, they usually have unacceptable performance at Ku-band frequencies. Since the wavelength at Ku-band is approximately 1/3 the length at C-band, the circular curvature creates three times the phase error at Ku-band as it does at C-band.
While the background discussion has been focused primarily on C-band and Ku-band antennas, because of their popularity at the present time, it will be understood that other frequency band antennas may become popular in the future. In fact, at the present time some signals in higher frequency bands are being considered. For example, 18 GHz signals (in the upper Ku-band or sometimes considered to be in the K-band) and 30 GHz signals (in the Ka-band) are presently experiencing some limited use. It is of course intended that all such frequencies and bands be included in the present invention.
Accordingly it is highly desirable to provide an antenna assembly which solves the above described problems.
It is an object of the present invention to provide a new and improved multi-feed, multi-band antenna.
It is another object of the present invention to provide a new and improved multi-feed, multi-band antenna including multiple feeds each capable of C-band and Ku-band reception, and capable of being positioned two degrees apart.
It is another object of the present invention to provide a new and improved multi-feed, multi-band antenna which is small, light, and which is inexpensive and easy to use.
It is still another object of the present invention to provide a new and improved multi-feed, multi-band antenna which can be easily and inexpensively mounted.
It is a further object of the present invention to provide a new and improved multi-feed, multi-band antenna which is sufficiently inexpensive and small to allow the installation of multiple antennas, if needed, without unduly imposing mounting area and cost restrictions and problems.